Method of forming a refractory metal rocket nozzle



Jan. 18, 1966 B. E. KRAMER 3,229,359

METHOD OF FORMING A REFRACTORY METAL ROCKET NOZZLE Original Filed July 5, 1962 INVENTOR BRUGE E. KRAME ATTORNEY United States Patent 3,229,359 METHOD OF FORMING A REFRACTORY METAL ROCKET NOZZLE Bruce E. Kramer, Rte. 4, Box 216, Loveland, Ohio Original application July 5, 1962, Ser. No. 207,829, now Patent No. 3,170,289, dated Feb. 23, 1965. Divided and this application Apr. 30, 1963, Ser. No. 281,853

3 Claims. (Cl. 29157) This application is a division of US. application No. 207,829, filed July 5, 1962, and now US. Patent 3,170,289.

The present invention relates to high temperature structural materials and methods of fabricating articles therefrom. More particularly, the invention relates to rocket nozzles formed entirely from refractory metal materials.

With the advent of solid propellant rocket engines, the extremely high temperatures and gas velocities generated have created a need for a temperature-resistant, erosion-resistant, high-strength, lightweight nozzle.

One of the prior art approaches to solve this problem is to construct the nozzle out of standard metals such as steel or aluminum and to circulate various coolants around the external surface. However, this nozzle has not proven satisfactory since it was too heavy, and demanded a complex system to circulate the coolant. The usual approach was to fabricate the body of the rocket nozzle out of lightweight insulative material such as graphite or plastic. Such insulative material was then coated on its inside surface with a high melting material such as tungsten to resist the temperatures and forces of the expelled combustion products of the propellant reaction. Such nozzle systems have series drawbacks and usually failed because there was little or no physical bond between the coating and insulative backup material, there was a mismatch between the coefficients of expansion of the materials and the insulative material was physically weak or broke down thermally.

Accordingly, it is an object of the present invention to provide a nozzle that is capable of use under extreme temperature conditions.

Another object is the provision of a nozzle that is not subject to failure in use due to mismatch of coefiicients of expansion.

A further object is to provide a nozzle that will resist the eroding forces of the high velocity gas stream.

A further object is to provide a method of constructing a nozzle that is simple, reliable and relatively inexpensive.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 shows a sectional view of a preferred embodiment of the invention; and

FIG. 2 illustrates a section of the device taken on the line 22 of FIG. 1 looking in the direction of the arrows.

Referring now to the drawings there is shown in FIG. 1 a nozzle 3 constructed of an interior shell 4 composed of a series of longitudinal strips 4a of tungsten or tantalum. Since the circumference of the nozzle is considerably reduced at the throat section, the width of longitudinal strips 4:: must be correspondingly reduced at that point, as shown by Dalgleish in US. Patent No. 2,976,679. Said shell is covered with a coating 5 of erosion resistant material such as tungsten, tantalum carbide and hafnium carbide. The shell is supported by, surrounded by, and attached to a corrugated backup liner shown as corrugations 6 on FIG. 2. The corrugations can be joined to an outer liner 7 of suitable material and the spaces between the corrugation 3,229,359 Patented Jan. 18, 1966 and the outside liner can be filled with suitable heat resistant material 8 such as ceramics and plastics.

FIG. 2 illustrates more clearly the construction of the nozzle wherein a plurality of strips 9 of tungsten or tantalum are joined by tantalum rivets 10 or are sprayed tungsten to the interior lands of the corrugations 6 to form the inner shell 4.

The following describes the fabrication process. Tungsten or tantalum sheet is hot rolled through a set of parallel gears with tapered teeth to provide a corrugated sheet which is then formed to the nozzle shape; the corrugations running in a longitudinal direction. The sheet is then joined by arc sprayed tungsten or by tantalum rivets, for example. Strips of sheet tungsten or tantalum are then joined to the interior lands of the corrugations. By longitudinally joining together the interior lands of the corrugation the inside liner of the nozzle is formed. The inside liner is then coated with are sprayed tungsten, hafnium carbide or tantalum carbide which forms a coating of erosion resistant material and also joins together the strips of sheet metal. The sprayed coating may optionally be vacuum sintered. The outside corrugations may be filled with suitable ceramic or plastic to stiffen and provide insulation. The outer shell is attached to the corrugations and the inside diameter may then if desired be ground to a smoother surface.

The apparatus by which the above steps may be performed is not critical nor part of the present invention. The corrugator can be any one of those commonly available in the art such as one similar to the one disclosed by Pappelendam in US. Patent No. 2,746,139. The are sprayed tungsten can be accomplished by electric arc furnaces commonly known or by a plasma stream apparatus such as that disclosed by Giannini in US. Patent No. 2,922,869. As is well known, tungsten melts at 6200 F. Though tantalum melts at 5400 F., 800 F. lower, it is more workable at room temperature and is thus easier to construct a nozzle out of this material. Of the spray coated materials, tungsten has proven most satisfactory and a 0.150 inch coating which was utilized in a solid propellant rocket engine did not come near its melting point. The liner is formed of 0.060 tungsten or tantalum sheet, but the corrugated sheet can be thinner. It should be understood that since the coeflicients of expansion and melting points of these two metals are so similar that the liner or corrugated backing may be made of either interchangeably, tantalum being preferred for uses below 5400 F. and tungsten being required for heats above 5400 F.

Thus, it is readily obvious that the nozzle is constructed completely out of refractory materials of extremely high melting point and erosion resistance. The mismatch of coefiicient of expansion is obviated since the materials 'have similar coefficients of expansion. Even the joining materials are refractory metals, i.e. tantalum rivets or arc sprayed tungsten. The are sprayed tungsten can also be used to coat the inner surface of the liner and concomitantly this coating will weld the seams between the strips as it forms the smooth inner surface. It should be understood that although the corrugations have been shown to run longitudinally, it is also permissible to have the corrugations run horizontally and then join the longitudinal strips of refractory metal thereto.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A method of forming a refractory metal rocket nozzle comprising in combination the steps of corrugating a hot sheet of said metal, forming said corrugated sheet into the shape of a nozzle, joining the open seam of said sheet, attaching a plurality of strips of said metal longitudinally to the axis of the nozzle to said corrugated sheet so as to form an inner liner, and coating said inner liner with an erosion and heat resistant material.

2. A method of forming a rocket nozzle substantially out of refractory metal comprising in combination the steps corrugating a heated sheet of said metal, forming said corrugated sheet into the shape of a nozzle, joining the open end of said sheet, attaching a plurality of metal strips to said corrugated sheet longitudinally to the axis of the nozzle so as to form an inner liner, and coating said inner liner with an erosion and heat resistant material selected from the group consisting of tungsten, hafnium carbide and tantalum carbide.

3. A method of forming a rocket nozzle substantially out of refractory metal comprising in combination the steps corrugating a heated sheet of a metal selected from the group consisting of tungsten and tantalum, forming said corrugated sheet into the shape of a nozzle, joining the seam of said formed sheet, attaching a plurality of strips of a metal selected from the group consisting of tungsten and tantalum to said corrugated sheet longitudinally to the axis of said nozzle so as to form an inner liner and coating said inner liner with an erosion and heat resistant material selected from the group consisting of tungsten, hafnium carbide and tantalum carbide.

References Cited by the Examiner OTHER REFERENCES Porter, H. B.: Rocket Retractories, Naord Report 4893, Note 1191, Aug. 26, 1955, Reprint by Ofiice of Technical Service, Department of Commerce, PB 131503, pp. 11-34.

WHITMORE A. WILTZ, Primary Examiner.

J. D. HOBART, Assistant Examiner. 

1. A METHOD OF FORMING A REFRACTORY METAL ROCKET NOZNLE COMPRISING IN COMBINATION THE STEPS OF CORRUGATING A HOT SHEET OF SAID METAL, FORMING SIA CORRUGATED SHEET INTO THE SHAPE OF A NOZZLE, JOINING THE OPEN SEAM OF SAID SHEET, ATTACHING A PLURALITY OF STRIPS OF SAID METAL LONGITUDINALLY TO THE AXIS OF THE NOZZLE TO SAID CORRUGATED SHEET SO AS TO FORM AN INNER LINER, AND COATING SAID LINER LINER WITH AN EROSION AND HEAT RESISTANT MATERIAL. 